The Bay of Islands ophiolite suite was displaced from an oceanic environment and emplaced upon the continental margin of Eastern North America during Early to Middle Ordovician times. The displacement tectonics produced a dynamothermal aureole that is found at the stratigraphic base of each ophiolite thrust slice. Structural and chemical studies of the aureole rocks indicate that they were produced by polyphase deformation of tuffaceous sediments and volcanic rocks under conditions of relatively high heat flux. Calculations show that this heat could not all have been produced by friction, but that the overriding ophiolite slab must have been hot. High geothermal gradients necessary to satisfy such a model are to be expected only in certain oceanic environments.